Fire alarm system



Sept. 20, 1966 c. BLOCK ETAL FIRE ALARM SYSTEM Filed Feb, 5, 19

2 Sheets-Sheet 1 60 W m; FIG. 4 w

fiE I44 I J2 56 52 70 Z 1 GAO. P I 4220 H 64 I ME 5 I l A? l 50 10 \ja 4Z INVENTORS 1504 J. M/Vrz ATTORNEY-5 Sept. 20, 1966 c. BLOCK ETAL FIREALARM SYSTEM 2 Sheets-Sheet 2 Filed Feb. 5, 1964 United States PatentThis invention relates to fire alarm systems, and more particularly to awireless system utilizing the regular household or building or plantelectrical wiring.

The general object of the invention is to improve such fire alarmsystems. A more particular object is to provide a system in whichtemperature sensors may be located at any wall switch or wall receptacleor outlet. The sensor controls a fixed high frequency oscillator, theoutput of which is conveyed through the household wiring.

A further object is to so rniniaturize the transmitter or oscillatorthat it may be located inside the standard recessed wall box orso-called gem box ordinarily used to house the wall switch or wallreceptacle alone. In accordance with a further feature and object of theinvention, the switch or receptacle unit itself is made readilydetachable from the alarm transmitter, so that in the event of switchfailure for example, the switch may be replaced at negligible costwithout having to replace the more expensive alarm transmitter.

A further object of the invention is to provide an alarm and a fixedhigh frequency receiver controlling the alarm, the said unit beingadapted to be simply plugged into an ordinary wal=l receptacle. Thus,one or more such alarm units may be located at desired locations, andmay be moved from time to time from one location to another ascircumstances may warrant.

To accomplish the foregoing general objects, and other more specificobjects which will hereinafter appear, our invention resides in the firealarm system, and the elements thereof, and their relation one toanother, as are hereinafter more particularly described in the followingspecification. The specification is accompanied by drawings in which:

FIG. 1 is a perspective rear view of a transmitter embodying features ofthe invention;

FIG. 2 is a perspective from view without the cover plate and wall box;

FIG. 3 is a front view looking toward the cover plate;

FIG. 4 is a vertical section showing the transmitter and a wall switchhoused ina conventional recessed wall box, omitting the clamps for thewiring;

FIG. 5 is a front view with the transmitter combined with a receptaclerather than a wall switch;

FIG. 6 is a vertical section drawn in schematic form;

FIG. 7 is a wiring diagram for the transmitter; and

FIG. 8 is a wiring diagram for the receiver and alarm.

Referring to the drawing, and more particularly to FIGS. 7 and '8, thesystem comprises a fixed high-frequency oscillator, centered about atank circuit 12 and a transistor 14, and adapted to be readily connectedinto and to be energized from an ordinary household power supply line atterminals 16 and 18. There is also a suitable fire detector or sensorusually a temperature-responsive sensor such as a bimetallic element,indicated at 20, and this is connected between the line and theoscillator in order to energize and start the oscillator in the eventice of fire. The high-frequency output of the oscillator is coupled backto the power supply line, in this case by means of a coupling capacitor22 and a conductor 24.

There is also a fixed high-frequency receiver, shown in FIG. 8, thisbeing adapted to be plugged into the household power supply line at someother desired location, as indicated by the plug 26 and cord .28. Thereceiver is tuned to the same fixed frequency as the transmitter, bymeans of a tank circuit 30, and is coupled to the line through conductor32 and coupling capacitor 34 for the reception of high frequency. Thereis an electrically operated alarm 36, and a relay 38 having contacts 40which are in series with the 'alarm, and which are closed by a firesignal. Preferably the contacts are spring biased to close, and thereceiver output serves ,to hold the contacts open when no fire signal isreceived, but permits closing of the contacts when a fire signal isreceived.

In accordance with an important feature of the inven tion, thetransmitter is so shaped and dimensioned that it may be located togetherwith a wall switch or receptacle in a standard recessed wall box or gem"box previously receiving the wall switch or receptacle alone. Thusreferring to FIG. 3, the cover plate 42 is of usual size, but it has anopening 44 through which the sensor 20 is exposed, and another opening46 for the handle 48 of a wall switch.

Referring next to FIG. 2, the metal strap or adapter plate 50 carries aninsulation casing 52 which houses the transmitter. The sensor 20 passesthrough a hole in strap 50. The switch unit 54 is carried by the strap50 and is preferably detachably mounted, as is indicated by the cam orlock 56 on strap 50. The strap has the usual slots 58 which receivescrews attaching the same to the box, and it has the usual threadedholes 60 for screws which hold the cover plate or wall plate.

The rear view of FIG. 1 shows how the transmitter casing -52 has aninverted U shape or is cut away at the bottom to receive the switchunit, omitted in FIG. 1. It also shows the terminal screws, in this casea ground screw 16 and a line screw 18. A leaf spring contact is alsovisible at 62.

Referring now to FIG. 4, the switch unit 54 is carried by the adapterplate or strap 50, it being detachable and locked in position by the camlock 56. It nests beneath the casing 52 and it has top and bottomterminal Screws 64.and 66. The top screw 64 is engaged by the leafspring contact 62, thereby connecting terminal 18 of the transmitter tothe switch.

FIG. 4 also shows how the fire sensor 20 is carried by transmittercasing 52 and passes through the strap 50 and cover plate or wall plate42. The latter is held on strap 50 by the usual screws 68, and the strap50 is secured to the recessed wall box by screws 72.

FIGS. 5 and 6 illustrate how the transmitter may be combined with a wallreceptacle or outlet instead of a wall switch. In FIG. 5 the cover plate74 has an opening 76 for sensor 20, and another opening 78 for an outletor receptacle 80, the latter being adapted to receive a conventionalplug, indicated in broken lines at 82 in FIG. 6. FIG. 4 is somewhatsimplified by omitting the screw clamps for the wiring coming into thebox, and FIG. 6 has been further simplified compared to FIG. 4. However,FIG. 6 does show how the outlet unit 80 nests .and are available on thecommercial market.

beneath or within the transmitter casing 52, and has terminal screws atthe top and bottom, the upper one being engaged by leaf spring contact62. The receptacle 80 is preferably detachably secured to the strap bymeans Such as the cam lock shown at 5 6 in FIG. 2.

It will thus be seen that the transmitter is dimensioned to be combinedwith a switch or receptacle, and to be housed in the standard recessedwall box of the switch or receptacle, the transmitter including atemperatureresponsive sensor 20 at the front, and having high-frequencyoscillator circuitry controlled by the sensor. The assembly is completedby a cover plate 42 or 74 which has an opening for the sensor andanother for the switch or receptacle. The transmitter and the switch orreceptacle have appropriate terminal screws at the back for line andground connections inside the box. In preferred :form, the transmitterassembly comprises an adapter plate 50 carrying an inverted U-shapedinsulation casing 52 which includes the sensor 20 at the front, thelatter passing through the adapter plate 50.

The casing houses solid-state semiconductor components for ahigh-frequency oscillator circuit and its D.C. supply, the circuit beingcontrolled by the sensor 20. The casing 52 further has terminal screws16 and 18 at the back for line and ground connections. The adapter plate50 is further provided with means such as the cam lock 56 to detachablyreceive a standard switch or receptacle unit, the latter preferablyhaving its terminal screws at the top and bottom. The casing 52 includesa downwardly urged spring contact 62 which bears against the top screwof the switch or receptacle for electrically connecting the line screw18 at the back of the casing to the switch.

Detachable switch and outlet units are already known One such unit isthe so-called Despard unit which is locked to the adapter plate or strapby a rotatable cam lock, such .as that shown in FIG. 2, but any otherdetachable unit could be employed. The reason a detachable unit ispreferred is that in the event of switch failure the switch unit may bereplaced at slight cost, without having to replace the alarmtransmitter.

In conventional house wiring the ground line, colored white, must bemaintained continuous. The hot line is colored black, or sometimes red.In FIG. 4 cable 86 supplies power, and cable 88 extends to an overheadlamp fixture controlled by switch 54. The ground or white conductor 84from BX or other sheathed cable 86 is connected to ground terminal 16.The ground or white Wire 90 of cable 88 is also connected to terminal16. The black wire 92 is connected to. terminal 18, and the black wire94 is connected to switch terminal 66. Cables 86 and 88 are anchoredsecurely to box 70 by means of conventional screw clamps, not shown. Itwill be understood that the leads 84, 90, 92 and 94 usually are longerthan here shown, so that they may be attached to the terminal screwswhile the assembly 52, 54 is outside the box, the assembly then beingpushed into the box and attached by screws 72, just as is done with aswitch or receptacle alone.

In FIG. 6 the ground or white wire 96 is connected to terminal 16. Thehot or black wire 100 is connected to the terminal 18, and through leafspring 62 connected to the upper screw 98 of the receptacle 80. Terminal16 is connected by means of jumper 102 to the terminal 104 of thereceptacle 80.

Referring now to FIG. 7, the spring contact is indicated at 62, and theswitch unit at 54. The circuit is essentially conventional, it beingminiaturized by the use of solid-state semiconductor elements. Theleft-hand part of the circuit, indicated by dotted line bracket 110, isa DC. power supply section utilizing a rectifier 112. The right-handportion of the circuit is the oscillator, centering about transistor 14,and utilizing a feed-back coil 114 coupled to fixed tuned tank circuit12. The output is de- 4 livered through output coupling capacitor 22.The circuit is connected to terminals 16 and 18, both for power supplyto the circuit, and for high frequency transmission from the circuit.

Referring now to FIG. 8, the receiver circuit also is preferablyminiaturized by the use of solid-state semiconductor elements. Theleft-hand portion indicated by dotted line bracket 116 constitutes a DC.power supply section based on rectifier 118. The received high frequencyenergy is supplied to a fixed tuned circuit 30 through a couplingcapacitor 34.

The receiver section is indicated by dotted line bracket 1-20, andincludes a transistor 122. The right-hand portion of the circuit servesto rectify the receiver output and to amplify the resulting DC. outputfor control of relay 38. -T his section is indicated by dotted linebracket 124, and includes voltage doubler rectifiers 126, 128, andtransient suppressor rectifier 130, as well as a power transistor 132used for DC. amplification.

In preferred form the alarm 36 is energized by a local battery 134. Thealarm may be a bell or buzzer or born or other such device. Theadvantage of -a local battery is in making the alarm fail-safe, so thatin the event of power failure the alarm will sound.

When a battery-operated alarm is used, the battery may be of theautomatically rechrageable type, and may be kept connected to the powerline. Thus, the battery charge is replenished whenever low, and thebattery is available to sound the alarm in the event of power failure,as well as in the event of fire. Then the alarm system will not bemistakenly relied on, when in fact there is no power .to energize it.

'In some cases the user may prefer that the alarm be powered directlyfrom the household wiring, in which case the conductors 28 (FIG. 8) mayextend to the alarm and thereby replace the battery 134. The system thenis failsafe to the extent that any failure in the receiver other thancomplete power failure will sound the alarm.

Although we have illustrated the transmitter associated with a wallswitch in FIG. 3, and with a receptabile in FIG. 5, in most cases a Wallswitch is preferred because it is located at greater height. A wallreceptable is equally good when the receptacle is an elevated one, butif the receptacle is low it is less effective. 'For the present pur poseit is preferred that the receptacle be at least two feet from the floor.

Apart from miniaturization, an additional advantage of using solid-statecomponents is that the circuitry is instantaneously responsive. Nowarm-up period is required.

In simplest form, the sensor is a bi-metallic disc or thermostat whichis temperature-sensitive. However, other sensors are known, responsiveto smoke for example.

An obvious advantage of the present system is that the sensor may belocated where desired, for example, in a garage, or in a basement nearan oil burning furnace. Multiple sensors may be provided, therebygreatly increasing the eifectiveness of the system. Similarly, multiplealarms (meaning the combination of receiver and alarm) may be provided.One alarm may be located in a bed room, to beheard at night. Anotheralarm may be located in a kitchen, to be heard during the day. The alarmcombination may be housed in an ornamental housing suitable to be'placedon a table or shelf, with a flexible cord like a lamp cord extending toa nearby wall outlet. The alarm may be designed to be hung on a hook ornail, and be similarly connected by its flexible cord to a convenientwall outlet. The alarm may be moved readily from one room to another;However, if desired the alarm unit may be permanently mounted in a boxdesigned for recessed 'wall mounting.

The system has been referred to as a household system, but this is notintended to exclude its application to an apartment house, or oflice, orindustrial plant. The term is used to distinguish from an alarm systemwhich is intended to sound an alarm at a very remote point, say afirehouse. The present alarm will function on wiring coming from thesame power line transformer. Thus, neighbors may have a common alarm,and a warning will be sounded in a neighboring occupied house in theevent of fire in a nearby vacant house. However, if the neighbors arenot cooperative, and prefer not to have a combined alarm, the system isreadily localized as much desired by the use of different fixedfrequency tuning. The frequency may be in a range of from 200 to 550kilocycles, and thus localized alarm systems may be provided whendesired by using different frequencies.

To summarize, the basic unit preferably consists of an adapter platewith a block or case permanently fastened to the rear of the plate. Thecase contains the circuitry and a bimetal thermal sensing element whichprojects through the adapter plate.- In addition, three terminalsproject from the case. Two are screw terminals Which are marked line andground, and one is a spring terminal which is joined internally to theline screw terminal. These are constructed to U.L. acceptablespecifications.

The spring terminal, the opening in the case, and an appropriate openingin the adapter plate, are so oriented and relatively located as toaccept and contain a standard Despard type of switch or receptacle. Thisis a standard commodity manufactured by many manufacturers of electricalswitches and hardware, and although it is available in many forms, theyare all mountable in the same openings and are retained by the same typeof lock or clip.

In any normal electrical installation the appropriate wires areconnected to the two screw terminals on the rear of the case and to theone exposed screw terminal on the 'Despard switch. The entire unit thenis inserted into the gem box, and fastened in the same manner as astandard switch or receptacle. A decorative cover plate with suitableopenings is then fastened to the adapter plate in the same manner as astandard wall plate.

If the temperature of the room rises to a level suflicient to activatethe thermal switch, a signal is generated by the transmitter and fedthrough all electrical lines in the building. This signal is immediatelyconverted into an audible signal by one or more similarly tuned receiverunits connected to the power line.

It is believed that the construction and operation of our fire alarmsystem, as well as the advantages thereof, will be apparent from theforegoing detailed description. It will also be apparent that while wehave shown and described the system in a preferred form, changes may bemade without departing from the scope of the invention, as sought to bedefined in the following claims. In the claims, the reference to atemperature-responsive sensor is not intended. to exclude other types offire detecting sensors.

We claim:

1. A transmitter assembly for a fire alarm system which transmitter isintended to transmit by high frequency carrier to a receiver-controlledalarm through the usual household power supply wiring, said transmitterbeing compactly dimensioned and being housed together with a powerwiring component in the standard recessed wall receptacle previouslyused for said wiring component, said transmitter including a temperatureresponsive sensor, and having high frequency oscillator circuitrycontrolled by said sensor, and a cover plate for said wall receptacle,said cover plate having an opening for the sensor and having anotheropening for the said wiring component, said transmitter and wiringcomponent having appropriate terminal screws at the back for line andground connections inside the recessed wall receptacle.

2. A transmitter assembly for a fire alarm system which transmitter isintended to transmit by high frequency carrier to a receiver-controlledalarm through the usual household power supply wiring, said transmitterbeing compactly dimensioned and being housed together with a powerwiring component in the standard recessed wall receptacle previouslyused for said wiring component, said transmitter including a temperatureresponsive sensor at the front, said transmitter having screws at theback for line and ground connections, a power wiring component havingconnection terminals at the back, means electrically connecting the linescrew of the transmitter to one terminal of the wiring component, saidtransmitter having D.C. supply and high frequency oscillator circuitrycontrolled by said sensor and utilizing solid state semiconductorelements, and a cover plate for said wall receptacle, said cover platehaving an opening properly located and dimensioned for the sensor andhaving another opening properly located and dimensioned for the wiringcomponent.

3. A transmitter assembly for a fire alarm system which transmitter isintended to transmit by high frequency carrier to a receiver-controlledalarm through the usual household power supply wiring, said transmitterbeing combined and housed together with a power wiring component in thestandard recessed wall receptacle previously used for said wiringcomponent, said transmitter assembly comprising an adapter platecarrying an insulation casing including a temperature responsive sensorat the front and passing through the adapter plate, said casing housinghigh frequency oscillator circuitry controlled by said sensor andutilizing solid state semiconductor elements, said casing having screwsat the back for line and ground connections, said adapter plate beingprovided with means to receive and hold the said wiring component, saidcasing having means electrically connecting its line screw to the saidwiring component, and a cover plate for said wall receptacle, said coverplate having an opening for the sensor and having another opening forthe wiring component.

4. A transmitter assembly for a fire alarm system which transmitter isintended to transmit by high frequency carrier to a receiver-controlledalarm through the usual household pow-er supply wiring, said transmitterbeing combined and housed together with a power wiring component in thestandard recessed wall receptacle previously used for said wiringcomponent, said transmitter assembly comprising an adapter platecarrying near one end an insulation casing including a temperatureresponsive sensor at the front and passing through the adapter plate,said casing housing high frequency oscillator circuitry controlled bysaid sensor, said casing having screws at the back for line and groundconnections, said adapter plate being provided near its other end withmeans to detachably receive and hold said wiring component, the latterhaving its connection screws at the top and bottom, said casingincluding a downwardly urged spring contact for bearing against the topscrew of the wiring component and electrically connected to the linescrew at the back of the casing, and a cover plate for said wallreceptacle, said cover plate having an opening properly located anddimensioned for the sensor and having another opening properly locatedand dimensioned for the wiring component.

5. A transmitter assembly for a fire alarm system which transmitter isintended to transmit by high frequency carrier to a receiver-controlledalarm through the usual household power supply wiring, said transmitterbeing combined and housed together with the power wiring component inthe standard recessed wall receptacle previously used for said wiringcomponent, said transmitter assembly comprising an adapter platecarrying near one end an inverted U-shaped insulation casing including atemperature responsive sensor at the front and passing through theadapted plate, said casing housing D.C. supply and high frequencyoscillator circuitry controlled by said sensor and utilizing solid statesemiconductor elements, said casing having screws at the back for lineand ground connections, said adapter plate being provided 7 8 near itsother end with means to detachably receive said References Cited by theExaminer wiring component, the latter having its connection screwsUNITED STATES PATENTS at the top and bottom, said casing straddling saidwiring component and including a downwardly urged spring con- 2,574,45811/1951 Atkinson tact for bearing against the top s r w f th i i 52,580,539 5 Goodwin 3403 10 ponent and electrically connected to theline screw at the i 1;; g g g g26 g2 b k f th t f e e ac 0 e g, n a cver pla e or said wall recep 3,204,245 8/1965 Dykaar 34O 220 tacle, saidcover plate having an opening properly located and dimensloned for thesensor and having another open- NEIL C. READ, Primary Examiner.

ing properly located and dimensione for the wiring com- 10 ponent. R. M.ANGUS, D. YUSKO, Assistant Exmminers.

1. A TRANSMITTER ASSEMBLY FOR A FIRE ALARM SYSTEM WHICH TRANSMITTER ISINTENDED TO TRANSMIT BY HIGH FREQUENCY CARRIER TO A RECEIVER-CONTROLLEDALARM THROUGH THE USUAL HOUSEHOLD POWER SUPPLY WIRING, SAID TRANSMITTERBEING COMPACTLY DIMENSIONED AND BEING HOUSED TOGETHER WITH A POWERWIRING COMPONENT IN THE STANDARD RECESSED WALL RECEPTACLE PREVIOUSLYUSED FOR SAID WIRING COMPONENT, SAID TRANSMITTER INCLUDING A TEMPERATURERESPONSIVE SENSOR, AND HAVING HIGH FREQUENCY OSCILLATOR CIRCUITRYCONTROLLED BY SAID SENSOR, AND A COVER PLATE FOR SAID WALL RECEPTACLE,SAID COVER PLATE HAVING AN OPENING FOR THE SENSOR AND HAVING ANOTHEROPENING FOR THE SAID WIRING COMPONENT, SAID TRANSMITTER AND WIRINGCOMPONENT HAVING APPROPRIATE TERMINAL SCREWS AT THE BACK FOR LINE ANDGROUND CONNECTIONS INSIDE THE RECESSED WALL RECEPTACLE.